Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $216.97   10.516%   $239.7866   $239.79   $239.80   $239.80  
  Purchase #2 $43.99   4.604%   $46.0153   $46.02   $46.00   $46.00  
  Purchase #3 $67.43   9.833%   $74.0604   $74.06   $74.05   $74.10  
  Purchase #4 $229.58   7.403%   $246.5758   $246.58   $246.60   $246.60  
  Purchase #5 $71.63   12.482%   $80.5709   $80.57   $80.55   $80.60  
  Purchase #6 $227.43   5.826%   $240.6801   $240.68   $240.70   $240.70  
  Purchase #7 $188.42   8.349%   $204.1512   $204.15   $204.15   $204.20  
  7 purchase totals = $1,045.45       $1,131.8403   $1,131.85   $1,131.85   $1,132.00